High temperature end fitting and method of use

ABSTRACT

Embodiments of a system and method for sealing an end of a flowline to an end fitting are disclosed. Such methods include providing an end fitting housing having a bore, wherein a portion of the bore has a tapered inner surface, inserting an open end of a flexible pipe into the bore, the flexible pipe having an external layer, to create a tapered annular space between the tapered inner surface and the external layer, and positioning a ring into the tapered annular space such that the ring radially contracts upon the external layer causing the external layer to deform to create a seal.

CROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This is a continuation-in-part of Ser. No. 09/689,075, entitledHigh Temperature End Fitting and Method of Use, filed on Oct. 12, 2000which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The invention relates in general to end fittings that retain andseal at least one open end of flexible pipe, and in particular to hightemperature end fittings.

BACKGROUND INFORMATION

[0003] A flexible flowline is comprised typically of several distinctconcentric layers that afford strength and flexibility to the flowline.The innermost layer, known as the carcass, prevents collapse of theflowline due to external hydrostatic pressure. The immediately adjacentlayer, known as the barrier, is constructed from a synthetic polymermaterial and serves to prevent content leakage. There may also besuccession of other layers of varying materials forming the overallcomposite of the flowline.

[0004] A flexible flowline may be utilized, for example, as a dynamicriser to couple a rigid flowline or another flexible flowline on theseabed to a floating vessel or buoy to convey production fluids such asoil, gas or oil/gas mixtures under pressure from an oil/gas well orplatform to the vessel or buoy. An end fitting can be utilized to couplethe flexible flowline at each end to an adjacent flowline or wellheadand the vessel or buoy.

[0005] One or more leak-tight seals contained in the end fitting hasbeen achieved in the manner of the prior art utilizing a seal ringwhich, for example, encircles and engages the external surface of thebarrier layer. This ring holds the barrier and carcass layers inposition within the end fitting by a frictional force generated from thepressure of the seal ring on the barrier layer.

[0006] While functioning well, problems with the foregoing seals havearisen inside the end fitting where the flowline and end fitting aresubjected to extreme fluctuations in temperature. Such extremes areknown to occur in the flowline and end fitting when they are, forexample, subjected to repeated changes in temperature as where, theflowline may be exposed to a temperature in excess 100° C. whenproduction fluid is conveyed through the flowline and subsequently maybe exposed to temperatures on the order of 0° C. from sea water whenflow of the production fluid is interrupted or discontinued.

[0007] Repeated thermal cycling in the foregoing manner can result in aloss of seal integrity due to stress relaxation and creep of the barrierlayer, followed by loss of compression at the seal. That is, with theseal area being highly stressed in compression, the flowline material atthe beginning of service is often in its most highly plasticized state.This, plasticized state, however, deteriorates with time untilultimately a loss in barrier thickness occurs and a state of equilibriumis reached. Once compression at the interface of the seal ring andbarrier declines to a low but non-zero level, loss of fluid content inthe flowline can occur. Phenomena such as thermal expansion and creepcan work to reduce or eliminate compression between the seal ring andthe polymer layer.

[0008] Despite recognition of the forgoing, it has not been previouslyknown how to satisfactorily eliminate the loss of tension and sealing ofthe flowline that can occur as described above.

SUMMARY OF THE INVENTION

[0009] This invention relates to an improved seal construction for anend fitting in which an open end of flexible flowline is to be received.More specifically, the invention relates to such an end fitting in whicha novel seal construction is provided capable of functioning tocompensate, offset or be unaffected by the adverse effects oftemperature swings to which the fitting is exposed in service.

[0010] These and other features, and advantages, will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings. It is important to note the drawings arenot intended to represent the only form of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a sectional view of a prior art end fitting containing areceived pipe end to be secured;

[0012]FIG. 2 is a sectional view of an exemplary end fitting containingthe improved seal unit construction in accordance with the invention;

[0013]FIG. 3 is a further sectional view of an end fitting containingmultiple seal constructions in accordance with the invention;

[0014]FIG. 4 is an enlarged sectional elevation of a seal hereof asutilized in the end fitting of FIG. 3;

[0015]FIG. 5 is a further enlarged sectional elevation of a sealconstruction at a different location in an end fitting in accordancewith the invention;

[0016]FIG. 6 is a sectional elevation of the seal housing of theinvention;

[0017]FIG. 7 is an enlarged sectional view of the encircled portion 77of FIG. 6;

[0018]FIG. 8 is a side elevation of the seal drive ring; and

[0019]FIG. 9 is a front elevation of the seal drive ring.

DETAILED DESCRIPTION

[0020] The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components, signals, messages, protocols, and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to limit the invention fromthat described in the claims. Well-known elements are presented withoutdetailed description in order not to obscure the present invention inunnecessary detail. For the most part, details unnecessary to obtain acomplete understanding of the present invention have been omittedinasmuch as such details are within the skills of persons of ordinaryskill in the relevant art.

[0021] Referring now to FIG. 1 of the drawings, there is illustrated aprior art end fitting designated 11 as disclosed, for example, in U.S.Pat. No. 5,639,128 incorporated herein by reference and available fromcommercial sources such as Wellstream, Inc. of Panama City, Fla.Briefly, the end fitting 11 comprises an annular body 13 adapted toreceive a flexible flowline 12 which comprises an interior or carcasslayer 14 and an exterior or barrier layer 16. An inner seal ring 18presses against the external surface of the barrier layer 16. A sleeve20 is received intervening between the carcass layer 14 and the barrierlayer 16. As shown, the seal ring 18 is compressed between the interiorwall surface of the annular body 13 and the exterior surface of thebarrier layer 16. The barrier layer 16 may be of a relatively softmaterial, such as polymer. The polymer may be of many different types,such as polyvinylidene fluoride (PVDF). PVDF has a relatively highthermal expansion coefficient and softens when heated to its maximumservice temperature. The sleeve 20 is placed below the seal ring 18 inorder to provide increased support for the compressive forces thatresult from deforming the seal ring 18 into the barrier layer 16. Thecarcass layer 14 is typically steel or stainless steel. Because thecarcass layer 14 and the body 13 are typically made from steel orstainless steel, their thermal expansion coefficient is much less thatthe barrier layer 16. Thus, under heat, the barrier layer 16 undergoesstress relaxation and the compressive forces transferred by the barrierare reduced. When cooled, the barrier layer 16 has lost some of itsability to recover and tends to shrink away from the seal ring 18, whichcould cause the connection to fail. On the other hand, some embodimentsmay not include a sleeve 20. In this case, the barrier layer 16 issupported by the carcass layer 14.

[0022] Referring to FIG. 2, there is an illustrated exemplary endfitting 10 incorporating one aspect of the present invention. Only thetop half of the end fitting 10 is illustrated in FIG. 2 because thelower half is symmetrical with the top half. The end fitting 10 includesan annular body 22, an inner collar 24, a body ring 26 and a barriersleeve 27. An interior surface of a counter-bore 28 in the body 22 andan exterior surface of a barrier layer 16 defines a wedge-like taperedrecess 30. A tapered wedge-shaped seal unit 31 is positioned within therecess 30. In the illustrative embodiment, the seal unit 31 comprises ahousing ring 32 and a housing drive-ring 34. The housing ring 32 may bemade from a compressible metal, such as an annealed corrosion resistantmetal, or a relatively hard polymer, such as polyphenylene sulfide orother deformable material compatible with fluids to be conveyed throughthe flowline. The housing ring 32 is generally wedge shaped so as to fitwithin the tapered recess 30. The housing ring 32 may have annulargrooves defined on its interior surface, such as annular groove 37. Acompressible seal 38, such as an elastomeric O-ring, may be positionedwithin the annular groove 37. Similarly, the housing ring 32 may have anannular groove 39 defined in its exterior surface. A compressible seal40 may be positioned annular groove 39.

[0023] In operation, a plurality of bolts 42 radially positioned aroundthe fitting 10 are tightened which causes the inner collar 24 to movecloser to the annular body 22. As the inner collar 24 moves closer, thedrive ring 34 is also moved closer to the annular body 22. The movementof the drive ring 34 causes an axial force on the seal unit 31 therebydriving the seal unit 31 further into the recess 30. The axial force onthe seal unit 31 also causes the seal unit to deform in a radiallyinwardly direction towards the underling barrier layer 16. Thisdeformation reduces the inside diameter of the housing ring 32 byforcing it onto a mating part of the end fitting which has a diametersmaller than that of the housing ring. This reduction in diameter of thehousing ring 32 causes the surface of the barrier layer 16 to deformuntil all gaps between the barrier layer 16 and the seal unit 31 areeliminated. Flexible seals, such as the seals 38 and 40, may also beused to further reinforce the seal in the event of additional relaxationof the barrier layer 16. As a result of the foregoing, the seal, orseals provide a means to seal against an irregular surface which may,for example, be an extruded polymer tube such as the barrier of thereceived flowline. By forcing the housing ring 32 onto the polymerbarrier surface 16, any surface irregularities are gradually reduceduntil the gaps between the housing ring and the barrier layer 16 aresignificantly reduced or eliminated. By reducing the gaps, the problemof potential extrusion of the flexible seals is also significantlyreduced.

[0024] Alternative embodiments are shown in FIGS. 3 and 4. For brevityand clarity, a description of those parts which are identical or similarto those described in connection with the first embodiment will not berepeated here. Reference should be made to the foregoing paragraphs withthe following description to arrive at a complete understanding ofadditional embodiment.

[0025] Referring now to FIG. 3, there is illustrated an end fitting 10which includes a tubular insert 43 secured via bolts 44 to a body 49. Acounter-bore 45 within the insert 43 accommodates receipt of theflexible pipe end 12 while an internally extending plastic cover 46encircles the pipe at an entrance 48. Corrugated wires 50 are secured inepoxy 52 to maintain the structural integrity of the unit. Containedwithin the end fitting are the inner seal unit 31 a with its housingring 32 a in a tapered recess 30 a. In this embodiment, there is also anouter seal unit 53.

[0026]FIG. 4 is a detail view of the seal unit 31 a and surroundingcomponents from the embodiment illustrated in FIG. 3. An interiorsurface 41 of a counter-bore defined in the tubular insert 43 and theexterior surface of a barrier layer 16 defines a wedge-like taperedrecess 30 a. The tapered wedge-shaped seal unit 31 a is positionedwithin the recess 30 a. In the illustrative embodiment, the seal unit 31a comprises the housing ring 32 a and a housing drive-ring 34 a. Thehousing ring 32 a is generally wedge shaped so as to fit within thetapered recess 30 a. The housing ring 32 a may have annular groovesdefined on its interior surface, such as annular groove 37 a. Acompressible seal 38 a, such as an elastomeric O-ring, may be positionedwithin the annular groove 37 a. Similarly, the housing ring 32 a mayhave an annular groove 39 a defined in its exterior surface. Acompressible seal 40 a may be positioned in the annular groove 39 a.

[0027] The operation of this embodiment is similar to the one describedwith reference to FIG. 2. When a plurality of bolts 47 are tightened, aninner collar 24 a moves closer to the tubular insert 43. As the innercollar 24 a moves closer, the drive ring 34 a is also moved closer tothe tubular insert 43. The movement of the drive ring 34 a causes anaxial force on the seal unit 31 a thereby driving the housing ring 32 afurther into the recess 30 a. The axial force on the seal unit 31 a alsocauses the seal unit to deform in a radially inwardly direction towardsthe underling barrier layer 16. This reduces the inside diameter of thehousing ring 32 a and the drive ring 34 a by forcing them onto a matingpart of the end fitting which has a diameter smaller than that of thehousing ring. This radial deformation causes the surface of the barrierlayer 16 to deform until all gaps between the barrier layer 16 and theseal unit 31 a are eliminated. Flexible seals, such as the seals 38 aand 40 a, may also be used to further reinforce the seal in the event ofadditional relaxation of the barrier layer 16.

[0028] Turning back to FIG. 3, one skilled in the art would realize thata similar situation occurs with respect to the outer seal unit 53. Whena plurality of bolts 57 are tightened, an outer collar 59 moves closerto the body 49. As the outer collar 59 moves closer, the housing drivering 55 is also moved closer to the body 49. The movement of the drivering 55 causes an axial force on the seal unit 53 thereby driving thehousing ring 54 further into the recess 56. The axial force on the sealunit 53 also causes the seal unit to deform in a radially inwardlydirection towards the underling plastic cover 46. This reduces theinside diameter of the housing ring 54 and the drive ring 55 by forcingit onto the plastic cover 46 which has a diameter smaller than that ofthe housing ring. This radial deformation causes the surface of theplastic cover 46 to deform until all gaps between the plastic cover 46and the seal unit 53 are eliminated. Flexible seals, such as the seals38 b and 40 b, may also be used to further reinforce the seal in theevent of additional relaxation of the barrier layer 16.

[0029] Some end fitting constructions may optionally also include amiddle seal unit similar to and axially between inner and outer sealunits 31 and 53. A detail of one such embodiment is illustrated in FIG.5, which illustrates a middle seal unit 60. A housing ring 62 is wedgedinto a tapered recess 64 of a collar 66. Included within the housingring 62 are opposite elastomeric seals 38 c and 40 c, which are similarto seals 38 and 40 described above. In this embodiment, a collar 67 canbe used to drive the housing ring 62 into the tapered recess 64 when aplurality of bolts 69 are tightened. As illustrated, once the housingring 62 is in place, the layer 16 deforms in a radially inward directionto accommodate the housing ring 62.

[0030]FIGS. 6 and 7 are section views of one embodiment of a housingring, such as the housing ring 32, which could be used in variousembodiments of the invention. Housing rings 54 and 62 could be of asimilar configuration but with different diameters. In one embodiment,the housing rings 32, 54, and 62 may be formed of hard metal, having across sectionally tapered section as illustrated in FIG. 6. An outsidesurface 72 of the ring may include one or more annular grooves, such asthe groove 37 in which to contain an elastomeric or flexible resilientseal, for instance an O-ring seal 38. Optionally, the housing rings canalso include one or more internal grooves, such as groove 39, on theinterior surface 78 for receiving an additional seal, such as an o-ringseal 40.

[0031]FIGS. 8 and 9 illustrate one embodiment of a drive ring, such asthe drive ring 34. The drive ring 34 is tapered similarly as the housingrings and include side cuts 80 to permit a controlled collapse in thecourse of being forced into its receptive recess behind a seal ring.

[0032] The resilient seals 38, 40 can be O-ring, cup seal, X-ring, orother suitable shape that can be coupled to a housing ring 32, 54 and62. On being forced into an encircling body with a matching taper buthaving a diameter smaller than that of the housing ring the insidediameter of the housing ring is caused to be reduced.

[0033] In this manner, sealing is provided and maintained against anyirregular surface which may be an extruded polymer tube such as thebarrier layer 16. By forcing the housing ring onto the polymer tube, anyirregularities are gradually reduced until gaps between the housing ringand the polymer tube are eliminated. By eliminating the gaps, thepotential for extrusion of the resilient seal is likewise eliminated.

[0034] Such construction can be used to seal high pressures sinceextrusion of the resilient seals is precluded. At the same time, theseal is superior to existing mechanical seals used in flexible pipes orhoses since mechanical seals require mechanical compression between theseal ring and the polymer layer. Moreover, the construction is notlimited to the fluid sealing layer of flexible pipe since it can bereadily applied to any extruded polymer layer of a flexible pipe orhose.

[0035] Significant for the foregoing is the use of a compressible metalseal housing ring or relatively hard polymer housing ring for the sealto deform the mating layer in such a way as to eliminate gaps. Thedesign can be used to seal high pressures since extrusion of theresilient seal is avoided. Moreover, it is superior to existingmechanical seals used on flexible pipes or hoses since mechanical sealsrequire mechanical compression between the seal ring and the polymerlayer. Phenomena such as thermal expansion and creep can work to reduceor eliminate such compression.

[0036] At the same time, such construction is not limited to the fluidsealing layer of flexible pipe, since it can be readily applied to anyextruded polymer layer in a flexible pipe or hose. By means thereof, aresilient seal applied directly to an extruded polymer layer, and housedin a metal housing which is forced onto the polymer layer to eliminategaps, the previous problems associated with temperature induced sealfailure in an end fitting is substantially if not completely eliminated.Furthermore, embodiments of the present invention work with flowlineswhich have barrier layers and flowlines which do not have barrierlayers.

[0037] By the above description there is disclosed a novel sealconstruction for an end fitting that contributes significantly to theoverall reliability of the end fitting per se. It achieves the intendedresult with only minor changes in construction so as not to contributeto any significant cost increase in manufacture of the overall endfitting. The virtues thereof can be readily appreciated by those skilledin the art.

[0038] Since many changes could be made in the above construction andmany apparently widely different embodiments of this invention could bemade without departing from the scope thereof, it is intended that allmatter contained in the drawings and specification shall be interpretedas illustrative and not in a limiting sense.

[0039] Although only a few exemplary embodiments of this invention havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments. Accordingly, all such modifications are intended to beincluded in the scope of this invention as defined in the followingclaims. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents, but also equivalent structures.

What is claimed is:
 1. A method for sealing an end of a flowline to an end fitting: providing an end fitting housing having a bore, wherein a portion of the bore has a tapered inner surface, inserting an open end of a flexible pipe into the bore, the flexible pipe having an external surface, to create a tapered annular space between the tapered inner surface and the external surface, positioning a ring into the tapered annular space to radially contract the ring upon the external surface causing the external surface to deform to create a seal.
 2. The method of claim 1 Wherein the positioning further comprises positioning a flexible O-ring in a groove positioned on an exterior surface of the ring to provide an additional seal.
 3. The method of claim 1 wherein the positioning further comprises providing a flexible O-ring in a groove positioned on an interior surface of the ring to provide an additional seal.
 4. The method of claim 1 further comprising providing a drive ring to urge the ring into the tapered annular space.
 5. The method of claim 1 further comprising coupling a collar to the end fitting to longitudinal prevent movement of the ring.
 6. A method of connecting a flexible flowline pipe to a an end fitting, the method comprising: forming a tapered recess between an exterior surface of the flexible flowline pipe and an exterior layer of the flexible flowline pipe, urging a seal unit longitudinally into the tapered recess, deforming the seal unit in a radially inwardly direction such that an interior diameter of the seal unit is reduced causing the exterior of the barrier layer to deform by the deforming of the seal unit.
 7. The method of claim 6 further comprising providing a flexible O-ring in a groove positioned on an exterior surface of the ring to provide an additional seal.
 8. The method of claim 6 further comprising providing a flexible O-ring in a groove positioned on an interior surface of the ring to provide an additional seal.
 9. The method of claim 6 further comprising providing a drive ring to urge the seal unit into the tapered recess.
 10. The method of claim 6 further comprising coupling a collar to the end fitting to longitudinal prevent movement of the ring.
 11. An apparatus for sealing an end of a flowline to an end fitting: a housing means having a bore, wherein a portion of the bore has a tapered inner surface for creating a tapered recess when an open end of a flexible pipe is coupled to the housing means, and a sealing means adapted to be positioned into the tapered annular space such that the sealing means radially contracts upon an external layer of the flexible pipe causing the external layer to deform to create a seal.
 12. The apparatus of claim 11 wherein the sealing means further comprises a flexible O-ring positioned on an exterior surface of the ring to provide an additional seal.
 13. The apparatus of claim 11 wherein the sealing means further comprises a flexible O-ring in a groove positioned on an interior surface of the ring to provide an additional seal.
 14. The apparatus of claim 11 further comprising a drive means for urging the sealing means into the tapered recess.
 15. The method of claim 11 further comprising coupling a positioning means to keep the sealing means in the tapered recess.
 16. An end fitting in which to receive an open end of flexible pipe, the end fitting comprising: a rigid component defining an internal central passage adapted to receive a flexible pipe, an internal annular tapered recess defined in the rigid component adapted to surround the flexible pipe, a seal unit having a generally triangular cross section within the recess at the inlet end of said passage to surround a received pipe, said seal unit within the recess of said component operatively effective to seal against leakage, said seal unit comprising: an annular member having a generally triangular cross section within the recess of said component to contiguously surround the periphery of a received pipe end, and at least one annular seal of resilient composition supported about the interior surface of said member for effecting a seal against at least the outer surface of a pipe end received in said component in which said annular member defines an annular groove in its inner surface in which said seal is contained for the seal thereof to engage the exterior surface of a received pipe end.
 17. An end fitting in accordance with claim 16 in which said seal unit includes a tapered, annular drive ring contiguously behind said annular member end that is wedged into said recess in response to a received axial force applied to said drive ring for displacing said annular member axially into the tapered recess of said component.
 18. An end fitting in accordance with claim 16 in which said component comprises an annular wall surrounding said annular member and said wall on its interior surface defines said tapered recess containing said seal unit.
 19. An end fitting in accordance with claim 18 in which said annular member defines an annular groove on both the interior and exterior surfaces thereof and a resilient seal is contained within each groove of said annular member.
 20. An end fitting in accordance with claim 17 in which said drive ring is adapted to diametrically collapse in the course of being forced into the tapered recess of said component.
 21. An end fitting in accordance with claim 20 in which said drive ring is of a hard metal composition and there is provided bolt means which when tightened apply said axial force to displace both said drive ring and said annular member into the tapered recess of said component.
 22. An end fitting in which to receive an open end of a flexible pipe, the end fitting comprising: an cylindrical body having a central passage adapted to receive an open end of the flexible pipe, wherein the central passage has an internal tapered surface which, when mated to the open end of the flexible pipe defines a recess, a housing ring adapted to be fully positioned within the recess, wherein the housing ring has a generally triangular cross section shape and is adapted to contiguously surround an outer surface of the flexible pipe, and at least one annular seal of resilient composition supported by the housing ring for effecting a seal between the outer surface of the flexible pipe and the internal tapered surface of the annular body.
 23. The end fitting of claim 22 further comprising an annular drive ring positioned contiguously adjacent to the housing ring, wherein the annular drive ring is adapted to receive an axial force for displacing the annular drive ring axially into the recess.
 24. The end fitting of claim 22 wherein the housing ring has a peripheral groove circumscribing an exterior side of the housing ring.
 25. The end fitting of claim 24 wherein the at least one annular seal is a flexible O-ring sealing member positioned within the peripheral groove such that a portion of the flexible O-ring sealing member is adapted to engage an interior surface of the annular body.
 26. The end fitting of claim 22 wherein the housing ring has an interior groove circumscribing an interior side of the housing ring.
 27. The end fitting of claim 26 wherein the at least one annular seal is a flexible O-ring sealing member positioned within the interior groove such that a portion of the second flexible O-ring sealing member is adapted to engage an exterior surface of the flexible pipe. 